The present invention relates to a patient controlled analgesia device for use with ultrashort acting opioid medication and a method for using the same.
Patient controlled analgesia (PCA) is a technique for providing pain relieving medicine to patients. Most commonly, it refers to intravenous, epidural, or subcutaneous administration of a liquid opioid via a pumping device with the patient having some ability to control the timing and quantity of drug delivery. Pumps currently in use for PCA generally give the clinician two parameters to set when prescribing a given drug for a patient. These include (1) a dose or bolus amount of drug administered whenever the patient presses a button and (2) a lockout interval which determines how soon after a bolus is administered a second bolus will be delivered if the patient presses the button again. If a patient presses the button before the lockout interval has elapsed, the PCA pump simply ignores the "request." The dose and lockout are programmed into the pump for an individual patient and drug combination. The dose is prescribed based on the clinician's assessment of the patient's opioid requirement (depending on weight, habituation, or other factors). The lockout interval is generally set depending on the time to onset of clinical effect of a given drug. The lockout interval is used to prevent a patient from giving himself or herself another bolus before the previous bolus has had a chance to take effect.
Sometimes a third parameter is programmed into a pump providing PCA. This is the flow rate of a continuous infusion of medication providing a background of opioid on top of which PCA is added. The continuous infusion is adjusted to provide the minimum amount of drug needed by a patient over time. The PCA component then allows the patient to administer extra (rescue or break-through-pain) doses as needed. This technique of using a continuous infusion along with PCA minimizes the requirement for a patient to push the button repeatedly as a bolus wears off. This is particularly useful at night when the patient's sleep would otherwise be interrupted regularly. Of note is the fact that currently used pumps do not generally allow the patient to adjust the rate of a continuous infusion. When they do, the patient must go through a series of programming inputs just like the clinician would when programming the pump initially.
PCA opioid administration, as described above has an inherent safety feature which prevents over dosage if the dose and lockout interval are set appropriately. Opioids have a side-effect of sedation. Therefore, if patients give themselves too much drug, they become sleepy and cease pressing the button. However, a supplemental continuous infusion, if set too high, can overcome this safety feature by providing more opioid to a sedated or even unconscious patient. This is why currently used pumps do not generally allow the patient to increase the rate of a continuous infusion.
The current method of providing patient controlled analgesia relies on the fact that boluses of commonly used opioids have a relatively long duration of action, i.e., an hour or more. However, the Federal Drug Administration (FDA)recently approved marketing of an opioid, remifentanil hydrochloride (hereinafter "remifentanil")marketed by Glaxo Wellcome, Inc., Research Triangle Park, N.C. 27709, under the trademark "ULTIVA". Remifentanil has a duration of action of only several minutes. Unless a patient's pain is intermittent and very short lived, current PCA pumps are not well suited for use with remifentanil. A patient with continuing pain, using a standard PCA pump to administer boluses of such a short acting opioid, would be required to press the button too often to be practical.
On the other hand, remifentanil or other ultrashort acting opioids can have significant advantages over longer acting opioids when administered by continuous infusion. The response to a change in an infusion flow rate would be very quick. This would be extremely useful when a patient's opioid requirement is not known or when the intensity of a patient's pain changes quickly. Currently, pumps are available which allow a continuous infusion to be adjusted and/or a bolus given. However, currently available pumps are not designed to have their flow rate controlled by a patient with a single push of a button as is possible for bolus PCA administration.